1. Field of the Invention
The present invention relates to an antenna device and a portable radio set, and more particularly, is suitably applied to those such as a cellular telephone, etc.
2. Description of the Related Art
The cellular telephone of this type has been decreased in size and weight so far in order to improve the portability. Thereby, a retracting/pulling out type of whip antenna device is positively developed as an antenna device provided for a cellular telephone. There is a cellular telephone configured as shown in FIGS. 1A and 1B as the cellular telephone of the above type.
In case of a cellular telephone 1 having the above configuration, a retracting/pulling out type of whip antenna device 3 is provided for a housing 2 made of a non-conductive member such as synthetic resin.
The antenna device 3 has an antenna section 6 provided with a rod antenna 4 made of a conductive wire rod and a helical antenna 5 formed by helically winding a conductive wire rod. The antenna section is set so as to be freely retracted and pulled out along a direction in which the antenna section 6 is pushed into the housing 2 shown by an arrow a at the upper end 2A of the housing 2 (this direction is hereafter referred to as retracting direction) and inversely, along a direction in which the section 6 is pulled out of the housing 2 (this direction is hereafter referred to as pull-out direction).
In the antenna section 6, a first power-supply member 7 made of a conductive member and having a protrusion 7A is electrically and mechanically connected to the lower end of the rod antenna 4 and a connecting portion 8 made of a non-conductive member is mechanically connected to the upper end of the rod antenna 4.
Moreover, a second power-supply member 9 made of a conductive member is electrically and mechanically connected to the lower end of the helical antenna 5 and mechanically connected to the connecting portion 8. Thereby, in the antenna section 6, the rod antenna 4 and the helical antenna 5 are mechanically connected each other by the connecting portion 8 but they are electrically separated from each other.
Moreover, the rod antenna 4 is covered with an antenna cover for the rod 10 and the helical antenna 5 is stored in a cap-shaped antenna cover for the helical 11 so that the antennas 4 and 5 do not directly contact a user.
A circuit substrate (not illustrated) on which various circuit devices including a transmission-reception circuit 12 and a matching circuit 13 are mounted and a shielding case serving as a ground member made of a conductive member for covering the circuit substrate are stored in the housing 2.
Moreover, an antenna power-supply terminal 14 made of a conductive member electrically connected to the matching circuit 13 is set inside of the upper end 2A of the housing 2 and only either of the rod antenna 4 and helical antenna 5 is electrically connected to the antenna power-supply terminal 14 when the antenna section 6 is retracted or pulled out.
Actually, in the antenna device 3, the antenna cover for the helical 11 is pushed in the retracting direction and made to contact the upper end 2A of the housing 2 to push the rod antenna 4 into the housing 2 and retract the rod antenna 4 in the housing 2 and electrically connect the second power-supply member 9 to the antenna power-supply terminal 14.
In addition, in this antenna device 3, under this state, the transmission-reception circuit 12 supplies the helical antenna 5 with power sequentially via the matching circuit 13, the antenna power supply terminal 14 and the second power supply member 9 so as to operate this helical antenna 5 as an antenna.
In addition, in this antenna device 3, at this time the rod antenna 4 is electrically separated from the antenna power supply terminal 14 by the connection section 8 so that it will not operate as an antenna.
On the other hand, in the antenna device 3, when the second antenna cover 11 is pulled in the direction to be pulled out under the state that the rod antenna 4 is retracted inside the housing 2, the rod antenna 4 is pulled toward outside from the upend 2A of this housing 2 and then the protrusion 7A of the first power supply member 7 is thrust onto the antenna power supply terminal 14 to bring this first power supply member 7 into electrical connection with the antenna power supply terminal 14.
In addition, in this antenna device 3, the transmission-reception circuit 12 supplies the rod antenna 4 with power sequentially via the matching circuit 13, the antenna power supply terminal, and the first power supply member 7 so as to operate this helical antenna 4 as an antenna.
Furthermore, in the antenna device 3, by electrically separating the helical antenna 5 from the antenna power-supply terminal 14 by the connecting portion 8, the antenna 5 is not operated as an antenna.
In this connection, to make the rod antenna 4 and helical antenna 5 operate as antennas, the impedances of the rod antenna 4 and helical antenna 5 are matched with the impedance of the unbalanced transmission line 16 by the matching circuit 13.
Moreover, the shielding case functions as ground for various circuit devices and moreover functions as an electrical shielding plate for preventing radio waves of external noise and radio waves emitted from the antenna section 6 from entering various circuit devices mounted on a circuit substrate.
Thereby, the cellular telephone 1 makes it possible to, at the time of pulling out the antenna section 6, transmit a transmission signal configured of a high-frequency signal from the transmission-reception circuit 12 to the rod antenna 4 through the matching circuit 13, transmit the transmission signal to a base station (not illustrated) through the rod antenna 4, and transmit a reception signal configured of a high-frequency signal transmitted from the base station and received by the rod antenna 4 to the transmission-reception circuit 12 through the matching circuit 13.
Moreover, the cellular telephone 1 makes it possible to prevent the portability of the rod antenna 4 from damaging by retracting the antenna 4 in the housing 2 at the time of retracting the antenna section 6, transmit a transmission signal from the transmission-reception circuit 12 to the helical antenna 5 through the matching circuit 13 under the above state, transmit the transmission signal to a base station through the helical antenna 5, and transmit a reception signal transmitted from the base station and received by the helical antenna 5 to the transmission-reception circuit 12 through the matching circuit 13.
Incidentally, in such a cellular telephone 1, multi-path phasing could take place when signals transmitted from a base station are received. Thus, as such a cellular telephone there is the one that is provided with an antenna device of a diversity reception system.
Here, FIG. 2 shows a basic configuration of the antenna device 15 of a diversity reception system, and for reception two antenna elements 16 and 17, for example, are provided, and these antenna elements 16 and 17 are brought into electrical connection with the switch 20 via the matching circuits 18 and 19 respectively, and the switch 20 is electrically connected with the reception circuit (not shown).
In addition, in this antenna device 15, the levels of the reception signals received by these two antenna elements 16 and 17 periodically are compared, and based on the result of this comparison, the switch 20 undergoes switch control to switch the antenna element 16 or 17 to be used for reception. Thus, the reception signal with a high level is selectively received so that multi-path phasing is reduced.
Incidentally, FIG. 3A as well as 3B where the same symbols for parts as in FIG. 1A as well as 1B corresponds each other shows a cellular telephone 22 which is provided with an antenna device 21 of a diversity reception system.
Such an antenna device 21 has a predetermined built-in antenna 23 disposed inside the housing 27, and this built-in antenna 23 is brought into electrical connection with the matching circuit 24.
This matching circuit 24 is brought into electrical connection with the switch 25 together with the matching circuit 13 to be brought into electrical connection with the antenna section 6, and this switch 25 is brought into connection with electrical connection with the transmission-reception circuit 12.
In addition, in this antenna device 21, a rod antenna 4 and a helical antenna 5 of the antenna section 6 are used as an antenna element for the dual use of transmission and reception, and the switch 25 undergoes switching control so that a built-in antenna 23 is used as the antenna element to be exclusively used for reception, and thus the transmission-reception circuit 12 is brought into electrical connection with the antenna section 6 at the time of transmission and the transmission-reception circuit 12 is brought into electrical connection with either the antenna section 6 or the built-in antenna 23 at the time of reception.
Thus, in a cellular telephone 22, the transmission signals are transmitted from the transmission-reception circuit 12 to the rod antenna 4 or the helical antenna 5 sequentially via the switch 25 and the matching circuit 13, and thereby these transmission signals are sent to the base station via the rod antenna 4 or the helical antenna 5.
In addition, in the cellular telephone 22, at the time of reception, the switch 25 rapidly undergoes switching control so that the reception signals received by the rod antenna 4 or the helical antenna 5 are transmitted to the transmission-reception circuit 12 sequentially via the matching circuit 13 and the switch 25, and the reception signals received by the built-in antenna 23 are transmitted to the transmission-reception circuit 12 sequentially via the matching circuit 24 and the switch 25 so that the levels between these reception signals are compared.
In addition, in this cellular telephone 22, when the level of reception signals received by the rod antenna 4 or the helical antenna 5 is high, the rod antenna 4 or the helical antenna 5 is brought into electrical connection with the transmission-reception circuit 12 via the switch 25, and when the level of reception signals received by the built-in antenna 23 is high, the built-in antenna 23 is brought into electrical connection with the transmission-reception circuit 12 via the switch 25.
Thereby, in the cellular telephone 22, at the time of reception, the reception signals received by the rod antenna 4 or the helical antenna 5 are transmitted to the transmission-reception circuit 12 sequentially via the matching circuit 13 as well as the switch 25, or the reception signals received by the built-in antenna 23 are transmitted to the transmission-reception circuit 12 sequentially via the matching circuit 13 as well as the switch 25.
Thus, in this cellular telephone 22, an antenna element of either any of the rod antenna 4 or the helical antenna 5 and the built-in antenna 23 is used so as to selectively receive reception signals with a high level and thus reduce multi-path phasing.
Incidentally, cellular telephones 1 and 22 in such a configuration are provided with, for example, an unbalanced transmission line 26 being configured by comprising a micro-strip line formed in a circuit substrate, and the transmission-reception circuit 12 is brought into electrical connection with the rod antenna 4, the helical antenna 5 or the built-in antenna 23 via the hot side of this unbalanced transmission line 26, and in addition, the ground side of this unbalanced transmission line 26 is grounded to the shield case.
In addition, in the cellular telephone 1 and 22, as shown in FIGS. 4A to 4C, the transmission-reception circuit 12 supplies the rod antenna 4, the helical antenna 5 or the built-in antenna 23 with power via the hot side of the unbalanced transmission line 26 so as to bring these rod antenna 4, helical antenna 5, or built-in antenna 23 into operation as an antenna, and then from the ground side of this unbalanced transmission line 26, the leakage current i1 flows into the shield case 27 which is approximately same potential with this so as to bring this shield case 27 into operation as an antenna as well.
But, in such cellular telephones 1 and 22, with any of the rod antenna 4, the helical antenna 5, and the built-in antenna 23 being thus brought into operation as an antenna, the shield case 27 operates as an antenna, and therefore a hand of a user grabbing the housing 2, which covers the shield case 27 via this housing 2, gives rise to a problem that the antenna characteristics of the cellular telephones 1 and 22 are deteriorated.
In addition, when the shield case 27 is operating as an antenna, the housing 2, which is grabbed by the user""s hand, approaches his/her head, and then this head will further cover the shield case 27 via the housing 2, and therefore the antenna characteristics of the cellular telephones 1 and 22 are further deteriorated, thus giving rise to a problem that the communication quality over telephones is deteriorated.
Moreover, the shield case 27, which operates as an antenna for transmission, radiates a power, and at that time a hand or the head of a user, which approaches the shield case, gives rise to a problem that the power per unit time and unit mass to be absorbed by a specific portion in a human body (so called Specific Absorption Rate (SAR)) increases.
In view of the foregoing, an object of this invention is to provide an antenna device as well as a portable radio set which can sizably reduce deterioration of the communication.
The foregoing object and other objects of the invention have achieved by the provision of an antenna device of a diversity reception system comprising: a first antenna element installed so as to be retracted and pulled out freely, a fixed second antenna element, an unbalanced transmission line for supplying the first and the second antenna elements with power, balanced-to-unbalanced transformation means for implementing balanced-to-unbalanced transformation action between this unbalanced transmission line and the first and second antenna elements, switching means for selectively switching connections of the unbalanced transmission line with the first and the second antenna elements and with only the first antenna element so that at the time of reception, the first and second antenna elements are brought into connection with the unbalanced transmission line via the balanced-to-unbalanced transmission line, or only the second antenna element is brought into connection with the unbalanced transmission line, and the switching means are arranged to bring the unbalanced transmission line into connection with the first and the second antenna elements via the balanced-to-unbalanced transmission line so that the unbalanced transmission line supplies the first and the second antenna elements with power via the balanced-to-unbalanced transformation means so as to operate the above described first and second antenna elements as an antenna.
Consequently, at the time when the first and the second antenna elements are caused to operate as an antenna, the balanced-to-unbalanced transformation action of the balanced-to-unbalanced transformation means prevents the leakage current from flowing via the unbalanced transmission line from the first or the second antenna element to the ground member onto which this unbalanced transmission line is grounded, and prevents the above described ground member from operating as an antenna so that deterioration of antenna characteristics in the vicinity of the human body can be sizably reduced.
In addition, in the present invention, in a portable radio set having an antenna device of a diversity reception system, a first antenna element installed so as to be retracted and pulled out freely in the antenna device, a fixed second antenna element, an unbalanced transmission line to supply the first and the second antenna elements with power, balanced-to-unbalanced transformation means for implementing balanced-to-unbalanced transformation action between this unbalanced transmission line and the first and second antenna elements, switching means for selectively switching connections of the unbalanced transmission line with the first and the second antenna elements and with only the first antenna element so that at the time of reception, the first and second antenna elements are brought into connection with the unbalanced transmission line via the balanced-to-unbalanced transmission line, or only the second antenna element is brought into connection with the unbalanced transmission line are arranged to be installed, and the switching means are arranged to bring the unbalanced transmission line into connection with the first and the second antenna elements via the balanced-to-unbalanced transmission line so that the unbalanced transmission line supplies the first and the second antenna elements with power via the balanced-to-unbalanced transformation means so as to operate the above described first and second antenna elements as an antenna.
Consequently, at the time when the first and the second antenna elements are caused to operate as an antenna, the balanced-to-unbalanced transformation action of the balanced-to-unbalanced transformation means prevents the leakage current from flowing via the unbalanced transmission line from the first or the second antenna element to the ground member onto which this unbalanced transmission line is grounded, and prevents the above described ground member from operating as an antenna so that deterioration of antenna characteristics in the vicinity of the human body can be sizably reduced.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.